Valve is taking L4D on the road/plane to several up in coming events for the public to play. Here there are:
Leipzig Games Convention, (Germany)
Festival du Jeu Video (France)PC Gamer Showdown (UK)
Penny Arcade Expo (Seattle, WA)
Penny Arcade will also get the unavailing of the Xbox 360 version. The came has already won some awards at e3 and will come out soon.